Tight Cluster: Going Heavy On Scale Management

San Jose Scale on Apple Trunk

Overwintering San Jose Scale Infestation on Apple Trunk

Synopsys: San Jose Scale, Quadraspidiotus perniciosus (SJS) continues to be a challenging pest to tree fruit growers throughout the Hudson Valley. If San Jose scale has been found at harvest, infested trees should without question be managed this spring to keep fruit from becoming overrun a second year. Be mindful that a tree carrying a few SJS damaged fruit last season will become an eruption of fruit injury the following year if left unmanaged. Significantly higher losses will certainly occur.

Finding a window to begin San Jose scale management with pre-bloom horticultural oil is the first and possibly the most important insecticide decision this spring. Beginning Easter Sunday morning and most of the day on Wednesday, April 15th, low wind conditions will optimize our opportunity for applications of oil at a 1% tank mix. Using higher rates or concentrating oil beyond 1/2″ green puts newly developing foliage at higher risk of phytotoxic injury and should be avoided, especially if temperatures drop much below 32F. If active Captan reside is present then oil should not be considered until residue has been significantly reduced. In this case Esteem® 0.86 EC, an IGR (Insect Growth Regulator) which does not require a penetrant, would be a good fit.

Complete coverage is essential, requiring higher volume and slower speed to get oil under and into the branch angles where SJS reside. As there is no known mechanism for SJS to develop resistance to this approach, oil then remains an important application, reducing the resistance potential of the insect to overcome our insecticide management tools while reducing the overall in orchard population of SJS. Relying on a single insecticide mode of action inevitably leads to insecticide resistance. This is especially so with endemic insects such as scale.

Introduction: SJS is native to China, first introduced into the United States in 1870s. By the early 1900’s, the pest had developed resistance to the arsenical insecticides used at that time, and over time becoming resistant to many commonly used pest management tools. Once established on its host, SJS infestations on the bark contribute to an overall decline in tree vigor, growth, and productivity. Fruit feeding induces localized red to purple discoloration around the feeding sites, decreasing
cosmetic fruit quality. Crawlers emerge almost continuously throughout the the season if infested trees are left unmanaged. Fruit infestations are then a constant threat once crawlers begin to emerge.

Biology: The infestation can begin by the ‘immature crawler’ life stage, being blown into the orchard from an infected apple tree or alternate host, to establish and become an endemic pest. The SJS will then begin infesting fruit in very low levels, often in a single tree. It will then overwinter in the orchard and resides is SJS has become established in your orchard last season, then a hard line management approach is essential. Eradication may require season long scheduling of directed applications to gain acceptable levels of control.

We have two to three generations of San Jose scale each year. The overwintering scale adults mature, take wing and mate during the bloom and petal fall period. First-generation crawlers begin appearing in early June in southern areas of NYS with emergence continuing for a month. They can be blown into un-infested orchards or adjacent blocks to infest the fruit. These crawlers develop into mature adults by late July. Second-generation adults appear from late July to early September; and, if a third generation occurs, it appears in late October to early November. The life cycle is completed on average in 37 days. Crawlers can usually be found from early June until a hard frost in the fall.

Other then apple and pear, San José scale have been found feeding and reside on a variety of fruit hosts including plum, cherry, peach, apricot and berries (e.g., raspberry, blackberry), as well as on nut-bearing trees (e.g., walnut) and many ornamental trees and shrubs (e.g., elm, maple, mountain-ash, serviceberry, juniper, white cedar, yew).

Overwintering SJS 'Black Cap' stage and damage to 2nd year apple stem.

Overwintering SJS ‘Black Cap’ stage and damage to 2nd year apple stem.

Monitoring for San Jose scale at tight cluster: The SJS is now in the ‘Black Cap’ overwintering stage. They can be observed on 1st and 2nd year wood more easily then older wood as the branches will have a purplish hue. Cutting into the cambium will expose this color more vividly. You can observe the yellow females and males beneath individual ‘scale’ coverings where they will complete development, mate and bear live young or ‘crawlers’.

Management: Pre-bloom (now) is by far the most opportune time to manage SJS. The overwintering immature stage, protected beneath the waxy covering are least protected from a spray application. However, developing foliage will increase ‘spray shadowing’ as the season progresses, reducing application effectiveness. A most effective timing during this period is delayed dormant, from the time silver tip begins to 1/2″ green.

Adult female beneath scale covering

To address the increasing SJS orchard infestations in the Hudson Valley, seasonal programs will require targeted applications of specific insecticides during three key periods of the season. Simply, in years to come, this insect has and will continue to cause sever losses in tree fruit. This is in part due to lack of pre-bloom oil use (often due to the presence of Captan fungicide), the industry loss of broad spectrum insecticides such as Penncap-M and post-bloom Lorsban as well as increasing likelihood of insecticide resistance. Addressing the overwintering population should begin at the first application of the season shortly after snow melt and navigable ground conditions. Ideal conditions often are not present until we are upon tight cluster or pink.

Management Options: Upon breaking dormancy, scale require air and begin metabolizing nutrients derived from feeding on the sap of the tree beneath their chitinous shell. smothering the insect using 1-3% horticultural oil can be very effective alone or in combination with other insecticides.

Interrupting the nervous system function through the use of Lorsban, still labeled in NYS while the use of Esteem 35WP and Centaur provide can control the insect, without the need for oil as a penetrant, to disrupt SJS development.

As we approach the San Jose scale pest control options available to us are numerous, and to succeed, multiple strategies should be considered.

Pre-bloom options included:
* Lorsban – does not require penetrant
* Esteem (DD-Pink): Insect growth regulator (IGR) – does not require penetrant
* Centaur (DD-Pink): Insect growth regulator (IGR) – requires penetrant
* Oil (DD-Pink) alone or with IGR’s
* Venerate XC (TC-Pink) – requires penetrant
* Sivanto Prime (DD-Pink)

Post bloom 1st and 2nd crawler emergence options are:
* Movento SC (spirotetramat) PF-1C (2-3 weeks prior to crawler emergence)
* Contact insecticides at nymph emergence (pyrethroids, OP’s, Neonicotinoids and pre-mixed formulations)
* Esteem
* Centaur
* Oil

Remember, the earlier the application against the overwintering black cap phase, the greater the likelihood of success. Coverage is critical in scale management, requiring a slow travel speed (2.5 MPH), low wind speed (5 MPH) and as close to a dilute application as possible. Increased foliage equates to “shadowing” and reduced coverage, which of course is the essential control component against the overwintering life stage.

Infestation levels that exceed just a few fruit at harvest in multiple blocks should be taken seriously. Even after a pre-bloom application is made, further management of populations should be considered as pockets of lingering scale in protected places are likely to remain in the tree canopy.

As a follow-up to pre-bloom control of SJS, consider the use of Movento 240SC at 6-9 oz./A plus a non-ionic penetrant such as 0.25% to 1% agricultural oil or LI700 to address the San Jose Scale fruit injury at pack out last year.

The active ingredient in Movento, spirotetramat, is taken into the foliage, systemically moving through plant tissue to stems, roots, and leaves to be fed upon by emerging SJS nymphs during emergence and feeding. Our research has found the single application of 9 oz./A at PF or two applications at 6 oz./A at PF and 2C will effectively control the 1st generation of the insect.

Softer insecticides: Esteem 35WP (pyriproxyfen) can be employed with or without oil, acting against the pest as an insect growth regulator (IGR), a unique mode of action for use against the immature scale. As the insect matures, the insecticide acts as a juvenile hormone analog to reduce the insect capacity to molt.

Centaur 0.7WDG (buprofezin), also an IGR does require a penetrating non-ionic surfactant such as 0.25% v/v oil to be effective.

Movento (spirotetramat), a systemic insecticide, cannot be used pre-bloom as per label restrictions, as there is insufficient foliage for effective uptake. Movento has been found to be most effective after PF in one to two applications, requires a penetrating non-ionic surfactant used at 0.25% (32 oz./100 gal.).

Incompatibility concerns over Captan use in early pest management programs for apple scab can be a formidable barrier when considering the use of oil. The possibility of phytotoxicity when using Captan near oil applications should be strongly considered when vying for a weather opportunity for SJS management windows.

Lorsban: NYS has revoked all tolerances for use of Lorsban beginning December 2021. The product can still be used in pre-bloom tree fruit insect pest management this season. On April 30th NYS legislators approved Senate bill S5343 and Assembly bill A2477B, which will bring about a ban on chlorpyrifos in New York beginning in 2021. This legislation is part of a larger environmental package and requires the approval of Gov. Andrew Cuomo’s (D) to put the new law into effect. The bill would ban all use of chlorpyrifos except for on apple tree trunks by Jan. 1, 2021 and ban the pesticide altogether by December 2021. The loss of this tool is very unfortunate.

A pre-bloom chlorpyrifos application made to the canopy has a considerable impact on rosy apple aphid (RAA), emerging obliquebanded leafroller larvae (OBLR), mullen and tarnish plant bug (MPB & TPB), European apple sawfly (EAS) and white apple leafhopper (WALH). Most importantly, if bees are brought into a block in a season of cooler temperature and delayed petal fall of later varieties, a pink application provides increased management of migrating plum curculio with less pressure to remove bees from a mixed block while active pollinators continue to work king flowers. It also provides a bit of insurance if beekeepers are delayed in removing hives from mixed variety blocks.

Be Aware: The active ingredient in Lorsban and the Lorsban generics is chlorpyrifos, which has a high bee-poisoning hazard. Judicious use of this product, well before bloom, is essential to reduce the risk to active pollinators.

My Opinion: The most important ause for chlorpyrifos should be relegated to trunk applications only targeting black stem and dogwood borer.

San Jose scale management at Pink

San Jose scale management at Petal Fall